CONTRACTURES AND INCREASE IN INTERNAL LONGITUDINAL RESISTANCE OF COW VENTRICULAR MUSCLE INDUCED BY HYPOXIA

This study was performed to determine whether hypoxia in glucose-free solutions can increase the electrical resistance of intercellular junctions in ventricular muscle. Internal longitudinal resistance (R(i)), mechanical tension, and transmembrane action potentials were measured simultaneously in cow ventricular trabeculae. The mean control value of R(i) was 265 ± 38 Ωcm (mean ± SE) at 34°C. After 1 hr of hypoxia in glucose-free Tyrode's solution, it had increased by 300 ± 41% (n = 11, P < 0.001). The rise in R(i) was closely related to the increase in resting tension (contracture). These effects were more pronounced during a second exposure to hypoxia and were potentiated by application of epinephrine, by increasing extracellular calcium concentration, and by increasing frequency of stimulation. Addition of glucose (50 mM) provided some protection against hypoxia. It is inferred that the increase in R(i) is entirely due to the increase in the resistance of intercellular junctions (electrical uncoupling). Intracellular calcium may be responsible for both the contracture and the uncoupling.